I've been investigating the feasibility of switching our heating/cooling from oil/electric to a geothermal system. We have plenty of room for horizontal loops and, through some contacts I have, I can get the loop excavation/backfilling done for free. Since the excavation cost is negligible and we are considering a future addition to the house, I'd like to oversize the loop field. Tentative plan is to run six 600ft loops, all terminated in a common manifold back at the house, with shutoff valves and pressure/temp ports for each loop. That would allow the "size" of the loop field to be changed as desired. Two questions: 1) There's only one path to the loopfield so all the lines would have to run in a common trench for the first 150'. It would be easy to dig deeper (10'?)and have one side of each loop run several feet below the other. How detrimental would it be to have all the lines in the common trench for that distance? 2) What factors go into the decision as to what diameter pipe to use in the loop field? The cost differential between 3/4" and 1" pipe is not significant to me. Ignoring price are there advantages to running 1" pipe for the loops instead of 3/4"? We intend to be in this house for many years so I favor higher initial costs that provide additional efficiencies even if the payback period would be in the neighborhood of 15-20 years. Thanks!

We don't know anything about your homes requirements. Don't know where you are located. Have no idea whether your design is adequate or oversized for ? ton unit.

Generally speaking you would run 11/4" header pipes to a manifold near the loop fields. If you do not wish to have the manifold out of reach you can have your free excavator bury a vault.

"oversized" loop fields offer very little in efficiency vs "right sized". To raise a field a few degrees may easily cost you in pumping power what you save in geo op cost.

Thanks Joe. I'm in upstate New York. As I understand it, I could get a "right sized" loop using either 3/4" or 1" pipe... just trying to decide if there's an advantage of one versus the other. Both appear as options in the Climatemaster loop design software. In my previous experience (not related to geothermal applications) we often found the increased friction loss when using smaller diameter pipes made the pumping much less efficient.

The two challenges I have are: 1) Accomodating needing a larger loop within a year or two (do to a planned addition to the house), and 2) the concern that I need to run both the "out" and "in" lines in close proximity for nearly 150 feet to get to the field. I'm trying to determine whether the impact of that is suffient to warrant insulating one of the lines or digging extra deep to try to increase separation... or is it not that big of a deal?

It really comes down to the final design of the system, house, type of soil, etc..

We do a majority of our work in Rochester, NY area, probably close to you and have been put into several situations where the houses are pretty far from the house.  some of the houses far from the house, we have put in the same trench, others layered, separate trenches, insulation, etc....run the numbers and see what happens.

Joe is right, figure out what your load is, meaning how much heat do you need to extract from the ground, then design your loopfield including the pressure drop calculations, then use 0.75" versus 1" in the the pressure drop calcs to see where you get with how much pumping power. BTW, why do you need p/t ports in each loop?

I would manifold in the field and run two main lines the 150' to house.

I just installed my system this past June. Due to geography of my site, I had to run 225' out and back to my loop field. I ran 1-1/4" pipe out and back in a single 1' wide trench. Out in the field, I have a concrete vault with a manifold and 6 loop circuit takeoffs. In design, we completely disregarded the 225' transit in terms of heat transfer and accounted for the full load in the 6 circuits. The field can cover the load. The transit pipe is some added cushion. Even though they are in the same trench, one hotter, one cooler, and may transfer some heat from one to the other, the earth temp is better than the average of the two loops, so net positive.

Posted By mtrentw on 22 Oct 2012 09:24 PM
I just installed my system this past June. Due to geography of my site, I had to run 225' out and back to my loop field. I ran 1-1/4" pipe out and back in a single 1' wide trench. Out in the field, I have a concrete vault with a manifold and 6 loop circuit takeoffs. In design, we completely disregarded the 225' transit in terms of heat transfer and accounted for the full load in the 6 circuits. The field can cover the load. The transit pipe is some added cushion. Even though they are in the same trench, one hotter, one cooler, and may transfer some heat from one to the other, the earth temp is better than the average of the two loops, so net positive.

How much gallons of flow do you need, how much pumping power do you need for that, and what does your pressure drop calcs show.

BTW, why do you need p/t ports in each loop?

I'm interested in instrumenting the system and would like to be able to monitor/test each loop individually. I expect some variation in the nature of the loops, such as burial depth, and have the opportunity to include a pond loop. Would be interesting to quantify the relative merits of each.

I would manifold in the field and run two main lines the 150' to house.

That's been a common suggestion which I'm giving consideration to. However, having the manifold in the house, with a shutoff value for each loop, would enable me to put in the additional loops I expect to need for the addition now and "turn them on" when required. Additionally, it would make the (admittedly unlikely) problem of a leak developing in one of the loops a non-issue since it could just be "turned off".

@ docjenser, I have 2 units, a 2 ton and 3 ton, each with its own pump. I think the numbers were around 25' of head with either running and near 40' with both. i went with two grundfos 26-150 3 speed pumps. i have played around a bit and settled with the 3 ton on med. speed and the 2 ton on low. i think it was 330 watt and 260 watt respectively is what the motor label says. it works out that i get about 3.5 gpm/ton with one pump running alone and about 2.5 gpm/ton when both run. @ OP. at my yard vault, i have shutoff ball valves on supply and return for each loop at the manifold. i actually had to isolate one loop to repair a leak at the geogrip fitting. my homemade concrete yard vault picture is attached.

You need quite some pumping power to run a 5 ton load through 225' of header pipe (I assume each way?), but given that you do not run both at the same time and only get to 600 watts when both are running, that might be acceptable. 40' of head is where you usually sit down and redesign your loopfield to get the pressure drop down.

Why would anyone pay for a manifold installation under the ground? Direct burial with fusion splice or even installed in a vault, it cannot be more cost effective than pulling the lines into the house,can it? One should be able to bring all ends of the ground loops into the "furnace" room, connect the manifold\flowcenter\HP for a minimal cost compared to the latter. No fusion splicing is required. I could go on and on about the benefits of the manifold in the house. (like isolating a loop leak without digging up the buried manifold) Another thing, why cant one just dig a little wider trench at the end of a horizontal loop and wrap the line around instead of fusion splicing a U fitting in the line? I helped install a complete Geo system this way. No "special" tools required. Not even a charge cart for filling and bleeding the loops. why cant one use Peak WWF (38% methanol\62%water) vs pure methanol, when methanol can only be purchased by the 55 gal drum for some, etc. If someone states the flowcenter pump will not assist in purging air from the ground loop, they are just plain wrong. (well, you need a micro bubble air separator connected in line with an automatic relief $74.00) All fittings were purchased from Home Depot, except the 1/8 T&P "needle. I Just want people to think outside the box sometimes. Crap, sorry for the hijac, I just saw the vault picture with the hillbilly feet and ...just started typing...:)

There are many philosophies of outside versus inside headering. It also depends on your equipment size and load requirements. Depending wether you have a good purge cart (2 HP+) and you have less than 8-10 tons of loop outside, I would always header outside, given the ease of installation. 2 core drills versus 6, 8, 10, 12 always wins me over. Insulation 2 headers is a pain, versus a simple straight pipe. A loop leak should not be a consideration since it should never occur. In this case it depended on how many lines you run out and wether you can design your header trench to contribute to the heat exchange. This is easier with a 2 ton system versus a 6 ton. This will also make a difference if you want to purge the loops with the flowcenter. You have to make sure the flow calculations are right.

Riderman,
Welcome!

What Doc has to say is so true.  We all have gotten to a point, together, to recognise that there is a huge diffrance in regional and local philosphy, on getting it done.  As long as it works to design being the most important.  It took me a while to get my brain wrapped around that.  In the end we are all better for the disscussions here.  We cover a 4 state area and our mantra is:  when in x, do as they do in x.
Eric

Thanks doc and water pirate for your advice.  With methanol in the loop, is there a recomended additive for preventing corrosion?  I cant remember if the flow center pump is cast Iron or not.  The Geo sites are all over the place on this subject..like just about every geothermal subject..lol :)

@ riderman. The geography of my site forces the loop field to start 250' away from the furnace room. This is a situation where a manifold/vault in the field is more cost effective than trying to bring all 6 loops out and back that narrow 250' area I had to run the trench.

The first rule of geothermal make up water is : municipal supply, if you are concerned about corrosion, monitor for issues and treat as they present, not shotgun at a problem you may never have. Geo on the loop side really needs to abide by the KISS principal for residential applications.
Eric